(1) Field of the Invention
The present invention relates generally to a flexible antenna system and, in a more particular preferred embodiment, to a buoyant cable antenna system with extended frequency range capability.
(2) Description of the Prior Art
Buoyant cable antennas are well known for use by submarines when the submarine is submerged. Such cables have been used to receive radio signals in the very low frequency and low frequency (VLF/LF) transmission bands. For instance, present buoyant cable antenna systems consist of a horizontal wire antenna for reception of signals in the range of from about 10 kHz to 130 kHz.
The buoyant cable antenna floats on the ocean surface and is deployed with a buoyant cable. The horizontal antenna element lies on the surface of the ocean and reception is limited by transmission line attenuation, amplifier gain and antenna characteristics. Seawater attenuation, antenna gain and frequency patterns limit the usefulness of the horizontal antenna element.
The buoyant cable antenna must be flexible because a submerged submarine preferably launches the cable antenna through a transfer mechanism which bends the cable through a six-inch radius. Because flexibility is required, buoyant cable antennas have employed a horizontal wire antenna element which receives signals from the fore and aft (front and back) direction relative to its deployment. The limited antenna gain pattern limits the reception capability of the buoyant cable antenna.
Various inventors have addressed similar problems related to buoyant cable antennas as discussed in the following patents. U.S. Pat. No. 5,933,117, issued Aug. 3, 1999, to the present inventor Erich M. Gerhard, is incorporated herein by reference, and discloses a buoyant loop antenna, deployable along a cable, which includes a core region comprising a plurality of annular ferrite beads. These annular shaped beads include a center hole and a generally concave first end and a generally convex second end. The ferrite beads are aligned with the concave end of one bead against the convex end of another bead. This allows the cable to flex while the beads maintain contact with each other, providing flexibility and resistance to crushing. The core region has a loop wire wrapped helically around it, forming the loop antenna. The loop wire element starts and ends at the same end of the core region, forming a loop. This loop allows transmission and reception in an athwart (side to side) direction. This wire loop antenna can be combined with a straight wire antenna (which provides reception in a fore and aft direction) to provide an omni-directional cable antenna assembly for VLF/LF frequency ranges.
U.S. Pat. No. 1,667,510, issued Apr. 24, 1928, to J. R. Coe, discloses a cable constituting an electrical conductor for high tension transmission lines having, in combination, a core comprising a plurality of short rigid members arranged end to end, and contacting wires of high electrical conductivity arranged spirally and side by side about said members.
U.S. Pat. No. 1,810,079, issued Jun. 16, 1931, to H. C. Jennison, discloses a conducting cable comprising a series of cups constituting a supporting means comprising a plurality of diaphragms and round contacting conductors spirally wound about the supporting means. The several cups have on their sides longitudinally extending surfaces aligning the cups within the spirally wound conductors. Adjacent end portions of adjacent cups are suitably nested so as to form ball and socket, joints between them.
U.S. Pat. No. 2,419,053, issued Jul. 3, 1942, to C. E. Bennett, discloses an electric cable in which the weight to volume ratio is such to render the cable buoyant. The cable comprises a continuous water pervious tubular member, conductor strands laid up about the tubular member or core, and a sheath of insulating material about the conductor strands. Floats are threaded upon the sheath and rigidly secured thereto. The adjacent ends of the floats are telescoping with each other while permitting relative angular movement to provide a flexible structure.
U.S. Pat. No. 4,978,966, issued Dec. 18, 1990, to Takizawa et al., discloses an antenna with a plurality of rod-shaped cores aligned in an end-to-end relationship and an antenna coil wound on the core array throughout its entire length. This arrangement permits the antenna to bend and fit a curved surface of a car where the antenna is mounted.
U.S. Pat. No. 2,428,480, issued Oct. 7, 1947, to H. A. Tunstall, discloses a tubular buoyancy element comprising a longitudinally flexible helix resistant to radial compression and a flexible waterproof covering enclosing the helix. Means comprising expanded rubber plugs are provided within the covering and have peripheral surfaces molded to and closely fitting the internal surface thereof for dividing the interior of the element into a plurality of closed compartments.
U.S. Pat. No. 3,117,596, issued Jan. 14, 1964, discloses a buoyant flexible hose comprising helically wound reinforcement means comprising a pair of tubular members in laterally adjacent relation and having longitudinally spaced convolutions and a plastic carcass enclosing at least a portion of the reinforcement means. The carcass comprises an inner tubular wall portion and an outer helically corrugated wall portion having the valley portions thereof secured to opposed portions of said inner wall portion. A portion of the reinforcement means is disposed between the peak portions of the corrugated outer wall portion and opposed portions of the inner wall portion. Sealed helical air spaces are formed between the portion of the reinforcement means and opposed surface portions of the carcass wall portions enclosing the same. The sealed air spaces are disposed on either side of the portion of the reinforcement means.
U.S. Pat. No. 3,823,249, issued Jul. 9, 1974, to Floessel et al., discloses a compressed gas insulated electrical high voltage conductor assembly comprised of a number of pressurized gas filled rigid straight sections arranged in end to end relation. Each section is constituted by a length of a rigid metallic tubular member which encloses and supports centrally therein a rigid portion of the electrical conductor. These rigid conductor enclosing section are joined together by means of short flexible sections of the tubular enclosing member and a corresponding flexible portion of the conductor thereby to enable the connected together rigid sections to be bent through an angle of substantially 180 degrees to facilitate transport from the fabrication point to a remote location for on site installation.
U.S. Pat. No. 5,561,640, issued Oct. 1, 1996, to W. C. Maciejewski, discloses a sonar array cable typically provided in lengths comprising hydrophone arrays and associated electronics and transmitter can components, with each cable length or section having one of each of these components housed therein. These sections are relatively stiff and unbendable, requiring that they be connected with relatively bendable intermediate segments. These intermediate segments are susceptible to excessive bending that can lead to failure of the wiring provided therebetween. The wiring in these intermediate bendable segments is provided in the form of a coil, each coil is rigidly connected to the transmitter and electronics in one cable section, and the other end of the coil being connected electrically to the wiring associated with the hydrophone array in an adjacent cable section. Each coil is encased in relatively soft urethane material, preferably in one portion of the bendable segment, another portion of the bendable segment having the coil connected at its other end to a relatively still urethane material associated with the transmitter can and associated electronics.
U.S. Pat. No. 4,346,953, issued Aug. 31, 1982, to Carnaghan et al., discloses a flexible coupling assembly for a radio antenna of a submarine buoyant cable antenna system is connected in a cable line that retains the characteristics of the cable as regards the outside diameter, flexibility tensile strength and electrical continuity. The assembly comprises flexible co-axial connectors at each end keyed to an insulator that press fit in a transition piece. The transition piece is press fit into the tubing by barbed type annular rings machined into the transition piece. Between the insulators and enclosed by the tubing are plastic pieces connected by a coil spring.
U.S. Pat. No. 5,745,436, issued Apr. 28, 1998, to S. H. Bittleston, discloses a semi-dry marine seismic streamer cable that consists of a number of connected streamer cable sections which each comprise a mechanical jacket surrounding a hollow core enclosing the seismic sensor and signal transfer means. Elongated axial stress elements for transmitting axial loads and a radial reinforcement member for relieving radial loads are provided in the jacket. The core is filled with a fluid or fluid saturated foam and the sensor means are mounted in the core by vibration isolating elements.
The above cited prior art discloses buoyant antenna cables which, at best, are limited in frequency range and which are limited as to the types of antennas which can be used therewith. Those skilled in the art will appreciate the present invention that addresses the above and other problems.